Measurement of autonomic function

ABSTRACT

The present invention is an article of manufacture and method for using same, comprising at least two sensors having a paired offset potential of below about +/−1.0 mV; and a data gathering device connected to the sensors capable of measuring the voltage difference between the sensors. The sensors preferably are AgCl coated Silver.

RELATED APPLICATION

This application is based on provisional application Ser. No. 60/837,658filed Aug. 15, 2006.

FIELD OF THE INVENTION

The invention relates to methods of detecting and quantifyingnociception and pain, and devices and components related thereto.

BACKGROUND OF THE INVENTION

The autonomic nervous system (ANS) governs the functioning of numerousorgans in the body of humans and other mammals. Yet there exists noquick, simple, inexpensive, or reliable test to measure the full rangeof autonomic function in an individual, nor its current state.

The two major components of the ANS are the sympathetic nervous system(SNS) and the parasympathetic nervous system (PNS). Nerves from bothusually innervate the organs they control. Thus organ performance is theresult of the interplay of both PNS and SNS. A measure of either SNS orPNS is not very useful in assessing the condition of the subject. Forexample, a subject may have high PNS tone without being relaxed becauseits effects are being offset by high SNS tone. Heart rate, for example,is determined by interplay between PNS and SNS. Both nerves innervateand affect our hearts. When a subject's PNS vagal nerves to the heartare cut, its heart rate rises and remains elevated.

A novel method is described herein to measure the moment-to-momentrelative dominance of PNS tone (sometimes also referred to as vagaltone) and SNS tone. The method is inexpensive, easily understood,consistent, reliable, as well as simple and quick to administer. It iscompletely passive and requires no voltage to be administered to thesubject, thus eliminating the possibility of side effects from theresultant current. It works well on both humans and animals.

The method gives a distinctive, “signature” reading for subjectsexperiencing any moderate to severe pain that has lasted for more than afew minutes, both in humans and other mammals. Therefore, it provides apreviously non-existent, objective description of pain. Currently, allpain is now measured by asking the subject questions about their pain(i.e., “On a scale of 0-10, how would you rate your pain?”). This isclearly subjective. Non-verbal patients cannot be evaluated by thesemethods. Thus health care providers are at a loss to measure pain inyoung children, advanced dementia adults, some stroke victims andintubated patients, as well as the rest of the animal kingdom. Preyspecies of animals (including horses and sheep) pose a particularchallenge because they are genetically programmed to mask their pain soas not to become the primary target of a predator. Even expensivethoroughbred racehorses are often the subject of vigorous debate bytheir caretakers regarding their pain status. Furthermore, a reliableand consistent objective measure of pain would prove useful to doctorswho suspect the patient is exaggerating or imagining his or her pain, aswell as to insurers who suspect malingering.

The method described herein works by recording a measurablephysiological correlate of ANS changes, namely the difference inelectrical potential between two sensors placed on the skin. Similar tothe Tarchinoff voltage measure of electrophysiology, it differs bysensing between sites of similar instead of high to low sweat glanddensities. Skin is innervated by nerves from both the SNS and PNS,which, respectively, increase and decrease physiological rates in tissueand organs throughout the body. These nerves are distributed relativelysymmetrically throughout the body but are not always activated in asymmetrical manner. With pain, for example, persistent pain fromanywhere in the body of moderate to severe intensity begins to raiseblood pressure (BP). This activates the baroreceptors in the carotidsinus artery. They trigger an increase in PNS (vagal) tone in an attemptto stop the BP increase and restore homeostasis. In addition, thisprocess triggers the release of endorphins, the body's own, naturalopioids which provide partial pain relief. This process is part of whatis known as Descending Nociceptive Inhibitory Control, or DNIC. Thisresponse is mediated primarily by the right cardiac vagal (PNS) nerve,not the left one. This nerve branches off and innervates other tissuealong the way. The result is slightly slower physiology on the rightside of the body. It has now been found that this includes thetwo-skin-site voltage difference effect. Accordingly, the voltage sensedon the right side of the body, with respect to the left, drops as PNStone rises through increased activation of the right cardiac vagalnerve.

PRIOR ART

Most Galvanic Skin Reflex measurement has been done by sensing the Fereeffect, so named after its discoverer. This is the change in the skin'sability to conduct electrical current due to sweat gland activity. Thereason for this method has been due partly to the relative ease,reliability, and consistency of measurements. This is due to therelatively large applied voltages used to measure the Fere effect, incontrast to the small, natural, body voltages of the Tarchinoff aspectof the GSR. In the case of the present invention, the magnitude of thevoltage difference between the right and left sites on the body, isoften smaller than the offset voltages of sensors which have beenstandard in the industry. Data gathered with high offset sensors wouldlead to inconsistent measurements and the conclusion that there was nouseful information to be obtained this way. The invention describedherein overcomes these deficiencies of the prior art methods.

Two posters have been presented at medical conferences showing anecdotalreports of such ANS shifts reflected in skin potential. (Ngeow, et al,Aug. 21-26, 2005), (D'Angelo, May 2006). This previous work did not usesensors which had been selected for their low offset potentials. Thepractitioners presenting these posters had been unaware of the role ofoffset potentials in these types of measurements, and it was notdiscussed in their posters. The form of sensor used to obtain the datapresented in the posters has produced a wide and changing variety ofoffset potentials due to a combination of factors. One was a lack ofconsistency in manufacture. Still another was a lack of consistency inuse. These sensors were of a cup style which required the examiner tofill the cups above the Ag/AgCl coated sensor surface to the brim of thecup with conductive gel. If the examiner fails to place the adhesivecollar with its hole directly above the cup, part of the collar willcover some of the electrode gel, blocking its area of contact with theskin. This may produce a smaller signal coupled to the system loadresistor. In addition, if the examiner fails to fill one of the cupscompletely to the brim, this may introduce a difference between the areaof contact of the two recording electrodes that also may produce asmaller coupled signal. Occasionally, good readings can be taken, suchas those selected for the posters, but they cannot be obtainedconsistently with the type of sensor methodolgy shown in the posterseven with trained personnel in the time conscious environment of aclinical setting. The proposed method solves that by using pre-appliedgel that has been spread evenly on each electrode during manufacture,producing much more consistent readings.

The present low offset voltage sensors invention can be used to trackthe progress of an individual during a series of treatments or duringhealing, due to consistent readings obtained by minute and consistentoffset potentials. This cannot be said of most other types ofelectrodes.

Most prior work involving the use of measuring sensors on the skin inorder to chart autonomic changes has been Galvanic Skin Resistance Work.This also uses electrodes on the hands, but the purpose and approach isof an entirely different type. In GSRes an external voltage is appliedto the subject's skin through a pair of sensors and the OSRes unitmeasures the current.

Levengood and Gedye in U.S. Pat. No. 6,347,238 utilize some of the samehardware as the disclosed invention but their method has greatlimitations. Levengood teaches electrodes against which the hand must bepressed neither of which is self-adhesive and both of which must bepressed against the hand or body by the physical force of tester orsubject. Since the magnitude of the coupled resistance loaded signal isaffected by the area of contact, even very slight variations in pressureproduce artifacts, namely variations in the recording. If skin surfacecontact resistances of the sensor pair, in some manner, tap into a bulk,internal, electrical field gradient, a voltage polarity reversal mayeven be brought about by a difference in physical force being applied tothe left versus right sensor. The self-adhesive sensor employed in thepresent invention eliminates this deficiency. Levengood's method isfurther limited by its use of solid metals. Virtually all solid metalsform a “half-cell” potential when they are in contact with a salinesolution such as the subject's perspiration. This well knownelectrochemical effect need not be further elucidated. The absolute andimbalance magnitudes of the half-cells for aluminum, the metal specifiedin Levengood, are amongst the largest for solid metals. This artifactcan overshadow the small signals being sought in the two-sensor sitevoltage measure. At a minimum, it will affect the numeric reading of thesite to site voltage. AgCl coated Ag sensors of the type employed in thepresent invention minimize this effect. Such low offset sensors are nottaught by Levengood.

Unlike prior art that deals primarily with the Fere effect and involvesactive addition of extraneous electrical current to the skin, thepresent invention, like Levengood, measures only the two site voltagemeasure. Leavengood does not teach the involvement of the ANS.Accordingly, the occasional false positive cannot be spotted.Occasionally a subject produces a positive reading despite being inmoderate to severe pain. If ANS indictors such as Heart Rate andDiastolic Blood Pressure are over 95, the examiner can take into accountthat SNS tone is obviously extremely high at the moment and thereforethe reading is unreliable. A chronic pain patient with pain of 7 on the0-10 VAS scale could still produce a positive reading under theseconditions. Thus the other cited prior art does not teach the disclosedmethod. None of the cited prior art deals with offset potentials of thesensors used. Without consideration of offset potentials, the weak twosite voltage difference cannot be measured accurately. Even somecommercial Ag/AgCl sensors possess offset potentials sufficient toseriously affect the voltage readings of the present method. However, byutilizing low offset potential electrodes (i.e. below 1.0 mV as in thedisclosed system, (and the lower the offset potential the better) asdescribed in more detail herein below, the voltage difference can bemeasured with consistent accuracy. Selected low offset potential sensorswere not taught in the prior art.

SUMMARY OF THE INVENTION

The present invention is an article of manufacture and method for usingsame, comprising at least two electrodes or “sensors” having an offsetpotential of below about +/−1.0 mV; and a data gathering deviceconnected to the sensors capable of measuring the voltage differentialbetween the electrodes. The sensors preferably are AgCl coated Silver.

It is an object of the invention to teach a device capable of measuringpain in a subject.

It is also an object of the invention to detect changes in the ANS.

It is a further object of the invention to teach a device capable ofmeasuring pain that uses low offset potential sensors.

It is another object of the invention to teach a device that sensesvoltage and does not pass a significant, exploratory current through thesubject.

It is yet another object of the invention to teach a pain measuringdevice that utilizes AgCl coated Ag sensors.

It is also an object of the invention to teach the use of a low offsetelectrode in a pain measuring device.

It is yet a further object of the invention to teach a device and methodwhich allows consistent quantifiable measurement of pain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a shows one example of the data gathering device of theinvention, a portable digital data gatherer with numerical LCD readout.

FIG. 1 b shows an example of the present invention for use with animals,wherein the electrodes are applied to identical spots on contralateralsides of a horse's neck.

FIG. 2 shows an example of use with humans wherein the electrodes areapplied to the center of the subject's palms.

FIGS. 3 a and b show examples of graphic display of a pain reading of ananimal, on a computer, showing the effects of a known ANS trigger,namely, the effect of a vacuum cleaner noise in proximity to a cat.

FIG. 4 shows epilepsy-like alterations in ANS activity.

FIGS. 5 a-d show dental pain and pain relief in a 51 year old malehuman, depicted on a strip chart recorder.

FIGS. 6 a-c show headache pain and pain relief in humans, depicted onstrip chart recorder.

FIGS. 7 a and b show pain and pain relief for horses, as shown on astrip chart recorder.

FIGS. 8 a and b show the reading of a lame horse before and afterhealing (shown on computer generated graph).

FIGS. 9 a and b show sensor offset potentials only measured by pressingtwo gelled sensors together gel to gel and connecting them to a datagathering device.

FIGS. 10 a and b show the magnitude distortion of subject readingscaused by electrodes with different amounts of offset potential.

FIGS. 11 a and b show the magnitude of the distortions of the sensors inthe prior art.

FIGS. 13 a-d show the consistency in readings taken with the AgCl coatedSilver sensors of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is an article of manufacture and method for usingsame. Comprising at least two sensors having an offset potential ofbelow about +/−1.0 mV; and a data-gathering device connected to thesensors capable of measuring the voltage differential between thesensors. The sensors preferably are AgCl coated Silver.

It is a key feature of the preferred embodiment that low offsetpotential sensors are utilized in the present invention. As mentionedabove, low offset potential sensors allow (the low artifact) detectionof the very (small voltages) generated as a result of SNS and PNSchanges in tone. Sensors of the prior art had higher offset potentialswhich act as noise artifact and confound the measurement of the small,desired signal voltages. The offset potential difference between thesensor pair of the sensors of the present invention should be belowabout +/−1.0 mV, and are preferably below +/−0.5 mV, and most preferablyabout +/−0.01 mV. Preferred sensors are model GS-26 from Bio-MedicalCorp. (Warren, Mich.), although any sensors meeting the criteria statedherein will be sufficient for the purposes of the invention.

In addition, the sensors of the present invention should have a coatingsufficient to conduct the small voltages due to SNS & PNS activationsbut should not create offset potentials of similar magnitudes. Aspreviously mentioned, aluminum sensors or other crystal lattices cancreate a higher offset potential. The most preferred coating for thesensor is an AgCl coating. The coating can deposited electroliticallydeposited and be of any thickness, although coatings of higherthicknesses are more durable and less prone to scratching. Othermaterials or coatings may be suitable, such as gold, so long as theyachieve the offset potential requirements of the present invention. TheAgCl compound is most preferred.

It is also preferable that the sensors be coated with a conductive gel.The conductive gel is preferably applied by a mechanical process thatallows for the gel to be applied in a consistent manner, and with aminimum of air bubbles. In most cases, this will mean that the gel ispre-applied utilizing a mechanical process at a factory. However, asused herein, the term pre-applied can refer to any process that allowsfor a consistent application of the conductive gel, i.e., a gel that isapplied with a consistent thickness across the sensor and in a manner sothat conductivity is consistent from electrode to electrode. This maymean that the gel is applied in a manner which creates a minimum of airbubbles or at least a consistent amount of air bubbles from sensor tosensor.

The sensors of the present invention will also most likely have a meansfor adhering the sensors to the subject. Any method of adhering thesensors to the subject is acceptable, as long as it does not interferewith the ability of the sensor to acquire the sensor to sensor voltage.For example, the electrodes could be taped to the subject. In apreferred embodiment, the sensor has a collar around the outer diameterof the electrode, which has an adhesive applied thereto. The sensors canbe affixed anywhere on the subject, so long as they are affixedcontralaterally in an identical manner. Preferably, the electrodes areaffixed in identical positions on either side of the body, for example,on the palms a humans' hands or opposite sides of their neck.

The size of the electrode depends on the type subject, and on which bodypart the sensor is to be attached. The device of the present inventioncan be used for either humans or animals. For humans, a sensor of 50 mmor less is desirable, and if the sensor is to be attached to the palm ofthe hand, a sensor of 10 mm is most desirable. For large animals such ashorses, sensors of up to 50 mm or larger may be appropriate. Therefore,it is anticipated that the size of the sensor will be selectedappropriately for the type of subject as well as the expected place ofplacement thereon.

The data gathering device of the present invention can be any devicesuitable for detecting the signals generated during the measurements.For example, the device can be an analog meter with a digital readoutthat simply reports the voltage differentials between the electrodes. Anillustrative example is seen in FIG. 1 a. Or, in the alternative, thedata gathering device can be a stripchart recorder typically used tomonitor EKG outputs. The data gathering device can also have a memorywhich allows it to record the data of one or more subjects over a periodof time. The data gathering device can potentially be linked with acomputer having software to maintain and analyze subject data. It canalso consist of an analog dial to display the strength of the reading.

In preferred embodiments of the present invention, the examiner usesdisposable, low-offset-potential biomedical sensors (offset of less than0.5 millivolts) with adhesive collars, a covering of conductive gelapplied at the factory, and an actual diameter of the sensor ofapproximately 10 mm, designed for use with humans. Each subject shouldbe allowed to rest quietly for ten minutes before the measurementprocess begins. Preferably, the subject refrains from coffee or otherstimulants for three hours before the measurement session. The presentinvention begins with the placement of the self-adhesive, extremelylow-offset-potential electrodes. On humans this may be advantageouslyachieved by placing one sensor in the center of each palm. The same siteon the palm should be used on each hand. See FIG. 2. However, othersites on the body can be used so long as care is taken to selectidentical sites on both left and right sides of the body. An alcoholswipe of the sites to remove excess skin oils (which can inhibitconductivity) may be performed prior to electrode placement. During themeasurement process, the subject should be asked to remain still andrelax. Abrasion of the skin can also be used to obtain still betterconductivity. To insure identical conditions, each palm is preferablytreated the same way to (e.g., use an identical number of strokes of thealcohol pad or abrasive on each palm, and use a different side of thepad for each palm). On short haired animals such as horses this can beachieved by using other contralateral electrode sites, such as bothsides of the neck, (see FIG. 1 b) which may require shaving of theelectrode site and preparation with an alcohol swipe. Alternatively, aconductive gel may be used to obtain valid readings through a coat ofhair or fur if it is not too thick.

During readings on humans, the subjects preferably sit upright, with thebacks of their hands resting on the top of their thighs. Care should betaken to avoid pressure on the wires or the electrodes. Subjects shouldthen be asked to remain still, close their eyes, and relax for theduration of the reading. If a non-digital data gatherer is used, such asa strip chart recorder, an ear clip ground should be employed. This isin the form of a silver clip attached to the right ear lobe, with a leadwire that plugs into the ground input receptacle of the recorder. Thisground wire substantially limits electrical interference by other peoplemoving around nearby in a busy clinical environment. For animal subjectsand non-verbal humans, the subject should be kept as stationary aspossible. In interpreting results, care should be taken to spot ANSdisruptions caused by impatience or anger on the part of the subjectfrom frustration or annoyance of being perhaps restrained for themeasurement. It should be noted that a minority patients, when measuredin the afternoon after lunch, have negative readings when in a pain freestate. Patient readings should be double checked or measurements done inthe morning if this phenomenon occurs for a particular patient.

To avoid the above problems with restraint, a hand-held measuring unitwith battery-powered data logger can be moved alongside the individualwhile they move about. Similarly, subjects with conditions that onlymanifest pain during movement (for example, walking or bending) can betracked while they move. Decreases in the values of readings duringmovement can be taken to indicate pain that is induced by the movement.

After preparation of the sensor site with alcohol pads, specialself-adhesive sensors with low offset potential are then peeled offtheir sheet and pressed onto the skin at the proper site. Theindividuals performing the measurement should run their thumb firmlyaround the top surface of the electrode's adhesive collar and press downon the metal electrode snap itself to assure that both electrodes arefirmly affixed. It is preferred that the entire gel coated metal sensingsurface be in contact with the skin on both sites on the subject. It isalso preferred to treat each electrode the same way in order to achieveidentical conditions on both contralateral sides. If, after removal ofthe electrodes, the examiner wishes to take another measurement, thealcohol swipe should be repeated to remove any adhesive residue on theskin from the first measurement.

Next the lead wires are attached to the electrodes by clips or snaps.The lead wires are connected across a load resistor of from 0.5 k to 500k Ohms, preferably 22 k Ohms, at a data gathering device such as a chartrecorder, digital data logger, or other device. The voltage differencebetween the lead wires in series with the voltage's source resistance(representing the “resistance-containing” voltage source between theleft and right sides of the body) produces a voltage drop across theload resistor which then “feeds” the data gathering device. The datagathering device can produce both numerical values and/or a continuousline on a volts vs time graph, either or both of which constitute thereading. The Y-axis displays the resistance-divider modified voltage ofthe incoming signal. Increases in voltage or decreases involtage-source-resistance between the left and right sides of the body,will increase the Y value. Sometimes the subject's reading or “trace”will be a fairly horizontal line on the graph. Often it will start outhigh above the Y=0 “baseline” (i.e. positive numerical values) and then,as the subject relaxes, begin to move downwards towards the Y=0baseline. Under normal circumstances, a trace will occur directly on theY=0 baseline if the voltage between the sensors is 0. Usually by the oneminute mark the trace will have stabilized at a “plateau” and remainrelatively steady. If this has not occurred, the measurer may wish tocontinue the trace for another minute.

After 60-120 seconds, the recorder can be switched off. The reading maynow be interpreted. While useful information may be obtained from theentire trace, the degree to which the trace may be above or belowbaseline at the end of the trace should be observed. The record of thetrace may be stored in a paper file or in a computer. The entireprocess, from site prep to storing the recording takes approximately 3-5minutes and can be performed by a minimally trained individual. Presenceor absence of moderate to severe pain can usually be confirmed with aglance at the graph to see whether the subject's trace is above or belowY=0. If it is below Y=0 (i.e. negative numerical values), the subjectcan be assumed to be in moderate to severe pain, unless otherconfounding factors are at work (ANS dysfunction, etc.) If the trace isabove Y=0, the subject can be assumed to be pain free or experiencingpain below a level of 4 on the 0-10 Visual Analogue Scale (VAS), as hasbeen determined by large numbers of measurements that have been taken onsubjects reporting their pain state on the 0-10 VAS at the time ofmeasurement.

This same protocol should be used even when the measurement is beingtaken for purposes other than the confirmation of the presence orabsence of significant pain (e.g., searching for disruptions in ANSbalance produced by other causes).

Lead wires from the electrodes should be connected to the data gathererin a pre-determined manner such that lower voltage on the right hand(vs. the left) will produce a trace below the zero baseline, or Y=0 andgive negative numerical values.

If analysis of more rapidly changing signals is desired, a data gathererwith sampling rates faster than 1 per second should be used along with acommensurate increased bandwidth “anti-alias” filter. A trace shouldthen be taken while the subject engages in controlled breathing orValsalva maneuver or other known vagal triggers for a minimum of oneminute. The data gatherer will record SNS tone increases in response toinspiration (breathing in) and PNS tone increases in response toexhalation. On a graphic display, the difference between the high peaksand the low valleys provide the lability of that individual's ANS. In agraphic display, or trace, of a subject's recordings taken during normalbreathing for diagnostic purposes, the distance of traces below the zerobaseline can then be expressed in terms of percentage of total ANSlability. If the display being used is numerical, adding the absolutevalues of the greatest positive voltage readings to the absolute valuesof the greatest negative voltage readings will equal the maximum ANSlability of the individual (e.g., positive 2.0 mV+negative 1.5 mV=3.5 mVtotal lability). This can allow the investigator to, for example in thecase of pain, estimate how significant the negative displacement of thetrace below Y=0 is for that given individual. This can be used toaccount for a decrease in the degree of ANS lability associated withage, and/or the fact that some individuals simply have more ANS lability(for example, are more excitable) than others. Therefore this controlledbreathing measurement procedure allows a quantitative estimate of thesubject's condition to be made without obtaining a prior baseline. Thebaseline reading can be obtained during controlled breathing when thesubject comes in for the first visit to obtain treatment orinvestigation of their condition. Similar analyses can be performedusing other known clinical vagal triggers such as the Valsalva maneuver.

When tracking of rapidly changing signals is not required, a lower rateof sampling (once every second to once every few seconds) along with anarrower bandwidth anti-alias filter will provide a smoother, moreeasily interpreted trace, one that eliminates much of themoment-to-moment swings caused by respiration. When faster tracking isdesired, the examiner may advantageously first measure with the fastsampling rate and broader filter during controlled breathing and savethis record. Next he or she may measure with the slower sampling rateand narrower filter and take the reading at the 60 second mark to allowcalculation of the sixty second reading as a percentage of totallability. This observed value can then be compared to establisheddatabases, thus indicating a range of pain levels associated with agiven degree of deflection from the neutral, zero baseline for thatgiven individual being measured.

Paper records from a chart recorder can be torn off and stored in thepatient's folder. With computer-linked digital data recorders, both thenumerical readings and the graph can be printed on paper and inserted inthe patient's chart and/or stored electronically as a file in thecomputer. Furthermore, such electronic files can be analyzed bysophisticated statistical analysis programs, and such files can bee-mailed to a colleague for consultation if the colleague has the samesoftware installed on his or her computer.

If grossly unexpected results are obtained, there may be one of twoproblems present. One of the sensors may have adhered to the subjectloosely. If this is suspected, simply repeat the measurement to confirm.However, if connections seem to be of equal quality on both sides, thenthe examiner should remove the sensors and check their offset potential.Even specially manufactured low-off set-potential sensors can sometimeshave a defective unit in a batch. Carefully peel off the sensors fromthe subject and place them together so that the exposed gelled metalsensing surfaces (i.e. the gelled surface contacting the skin) of thetwo sensors are precisely atop one another. Press them and theiradhesive collars firmly together so that the adhesive collars keep thegelled surfaces in contact. Connect lead wires to the sensors and take areading. Readings obtained should be on the order of less than 0.2 mV.If readings substantially above this are obtained, then the offsetpotential may be grossly affecting the subject's reading magnitude andthe entire measurement process should be repeated.

Problems of high offset potential may be due to the nature of thesensors or the chemical compound coating the sensors. Pure metalsgenerally form sizeable half-cell potentials. That is, interactionbetween the salt water of the subject's perspiration (always present onthe skin to some extent) reacts with the metal to generate a half-cellvoltage. This artifact can overwhelm the small signals being acquired inthe two-sensor-site measure of the present invention. At a minimum, itwill affect the numeric reading of the site to site voltage. AgCl coatedAg electrodes of the type employed in the present invention weredeveloped precisely to counter this effect. These are pure standardmetals, such as silver, but the area in contact with the skin contactinggel is coated with an electrolytically formed silver-chloride layer.These have much lower offset potentials than most other sensors. Howeverthe thin coats of AgCl are easily scratched and therefore it ispreferred to use disposable Ag/AgCl sensors in order to insureconsistency of readings.

However, even Ag/AgCl sensors may have offset potentials on the order ofseveral millivolts. This is measured by pressing two sensors togetherand measuring the effect. The site to site voltage difference measuredwithout skin abrasion in the present invention is often less than amillivolt. Thus offset potentials can overshadow this signal and produceerroneous results. Clearly, the use of low offset potential electrodesallows meaningful data to be obtained during the type of measurementsthat constitute the method described here.

There are numerous uses for the present invention including measuringthe effects of various agents on SNS and PSNS tone, including but notlimited to: beta blockers, atropine, scopolamine, beta-adrenergenicblockade, sedatives, anti-anxiety medications, analgesics, anesthetics,narcotics, and others. Thus the proposed method may help in titration ofmedicines and/or determining the effectiveness of a particularmedication for a given subject. The method may also help in diagnosingconditions that involve altered ANS function, including but not limitedto: certain types of hypertension, Parkinson's disease, multiplesclerosis, Guillain-Barre syndrome, and orthostatic hypertension of theShy-Drager type. In some of these disorders, changes in PNS tone may beuseful in quantitating the rate of disease progression and/or the effectof therapeutic intervention. Identifying changes in PNS tone may help inidentifying fetal and neonatal distress and identifying those at highrisk of sudden infant death syndrome.

EXAMPLES

For the examples described below the following procedure was followed:Unless otherwise noted, the examiner used disposable,low-offset-potential biomedical sensors model GS-26 from Bio-MedicalCorp. (Warren, Mich.), with adhesive collars, having a covering ofconductive gel applied at the factory. When humans were measured, thesubject was allowed to rest quietly for ten minutes before themeasurement process started. A self-adhesive, extremelylow-offset-potential sensor was placed in the center of each palm. Analcohol swipe of each palm to remove excess skin oils (which can inhibitconductivity) was performed prior to sensor placement. and an ear clipground was employed if other individuals were moving around a ChartRecorder based data gathering setup. The subject was asked to remainstill and sit upright, with the backs of their hands resting on the topof their thighs, and to sit in a relaxed position with their arms limp.When horses were measured, the horses neck was shaved and the sensorsplaced on both sides of the neck, (see FIG. 1 b).

The lead wires were connected at their opposite ends to a data gatheringdevice. In the case of the data generated for FIGS. 4 to 7, the datagathering device was a recorder available from Kipp & Zonen, ModelBD112, (Delft, Holland). For data generated for FIGS. 3, and 8-13, therecorder was a Biographs, LLC, PT-05 PainTree™. The device was switchedon, and data recorded for a period of 2-3 minutes. The machine wasturned off, the electrodes removed from the subject, and datainterpreted.

Example 1

FIGS. 3 a and b show examples of the graphic display of a reading on acomputer, showing effects of a known ANS trigger. Specifically, FIG. 3 ashows distress in a cat. The sensors were placed on the cat's paws. Thecomputerized trace shows a rise in sympathetic tone (upward movement onthe Y-axis) known to be associated with distress in animals caused byproximity of an operating vacuum cleaner. Vacuum was switched on at 107seconds (X-axis) and moved closer until at 140 seconds after measurementbegan, the cat fled the device.

FIG. 3 b shows a human doing controlled breathing: Trace rising andfalling (re. Y-axis) illustrates the known ANS effects of controlledbreathing. Inhalation causes a rise in sympathetic tone (rise in traceon graph) and exhalation causes a rise in parasympathetic (i.e. vagal)tone (fall in trace). This 41 year old female human was inhaling for 5seconds (x-axis), followed by exhaling for 5 seconds, for approximatelyone minute. This type of controlled breathing is a classic medicaltechnique used in the study of ANS function.

Example 2

FIG. 4 shows epilepsy-like alterations in ANS activity: Reading depictedon strip chart recorder is for a 75 year old male with sporadic,pronounced, and uncontrollable hand tremors. As is known to happen withsome types of epilepsy, the seizure-like activity occurs at the peak ofa rise in sympathetic tone (rise of trace on Y-axis) and is immediatelyfollowed by a strong rise in parasympathetic tone (shown by a fall insubject's trace on the Y-axis) as the body attempts to restorehomeostasis. This example depicts how the proposed method may helpdiagnose non-manifesting forms of epilepsy, as well as catchepileptic-like activity early in its development with a subject beforeit grows into full-blown seizures. Likewise, such measurements mighthelp the physician titrate the dosage of seizure medications.

Example 3

FIGS. 5 a-d show dental pain in 51 year old male human, depicted onstrip chart recorder. In FIG. 5 a, the subject reports substantial pain.Trace is well below the X axis, indicating moderate to severe pain. InFIG. 5 b, the same subject is shown 20 minutes after ingestion ofoxycodone (½ tablet of 5/500TA). Trace is rising slightly. In FIG. 5 c,70 minutes after oxycodone ingestion, half of trace is above X-axis.Subject reports significant pain relief. In FIG. 5 d, 180 minutes afteroxycodone ingestion, subject is pain free and trace is completely aboveX-axis in 3 separate measurements. Oxycodone is known to take 3 hours toachieve its full effect.

Example 4

FIGS. 6 a-c show headache pain in humans, depicted on strip chartrecorder using methods disclosed in U.S. Pat. No. 6,347,238. In FIG. 6a, a 35 year old female reports severe headache pain. Trace of readingis well below X-axis, indicating moderate to severe pain. FIG. 6 b showsthe same subject one hour after ingestion of Excedrin Migraine®medication. Subject reports that pain has greatly lessened. Trace isalmost back to X-axis. 135 minutes after ingestion of medication, FIG. 6c shows the subject is pain free and the trace is now well above X axis,indicating a pain-free state, which agrees with the subjectsself-report.

Example 5

FIGS. 7 a and b show pain and Pain Relief in Horses (shown on stripchart recorder). FIG. 7 a shows a 2 year old female horse sufferingpost-surgical pain, before prescribed analgesic injection. FIG. 7 bshows the same horse 6-7 minutes after prescribed analgesic injection.FIGS. 8 a and b show a lame horse before and after healing (shown oncomputer generated graph). FIG. 8 a shows a 3 year old lame male horsewith swollen, cut foot. FIG. 8 b shows the same horse one week later.Foot healed, lameness gone.

Example 6

FIGS. 9 a and b show pure offset potentials measured by pressing twosensor's sensing faces together and connecting them to the measuringdevice. There is no connection here to any subject. FIG. 9 a shows thatsensors with relatively high offset potential (0.75 mV) create theirown, large traces which decay over time, adding a changing level ofdistortion to readings taken on any subject. Often this voltagepotential can exceed the size of the voltage being measured in asubject. FIG. 9 b shows that sensors with very low offset potential(0.01 mV) add only a minimal and unchanging distortion, which is muchlower than the vast majority of two-sensor site readings from animal orhuman subjects.

Example 7

FIGS. 10 a and b show the distortion of subject readings caused bysensors with different amounts of offset potential. Subject: 51 year oldmale human with no pain.

FIG. 10 a shows a human subject in a non-pain state. The offsetpotential of the sensors used equals 0.01 mV. FIG. 10 b shows the samehuman subject, 8 minutes later. The offset potential of the sensors usedequals 5.0 mV. Note added distortion from high offset potentialcompletely changes the nature of the reading obtained from subject.

Example 8

FIGS. 11 a and b show the distortions of subject readings caused bysensors with different amounts of offset potential. Subject: 3 year oldmale horse with no known pain. FIG. 11 a shows the horse in a non-painstate. The offset potential of the electrodes used equals 0.01 mV. FIG.11 b shows the same horse 8 minutes later. The offset potential of theelectrodes used equals 4.2 mV. Note how the added distortion of the highoffset potential here has even changed which side of the X=0 baselinethe trace occurs on. In this case, this could have caused a pain-freestate to be mistaken for a painful state.

Example 9

FIGS. 12 a-d shows the inconsistency in four readings taken withreusable, cup-style, Ag+AgCl mixture sensors. All readings were taken onsame subject just minutes apart (FIG. 12 a, 9:15 P.M.; FIG. 12 b, 9:22P.M.; FIG. 12 c 9:39 P.M.; FIG. 12 d 9:47 P.M.). Note great variability.Subject was normal, healthy 54 year old white male, not in pain, andwithout ANS dysfunction of any kind. FIGS. 13 a-d show the consistencyin four readings taken with AgCl coated Ag sensors of the presentmethod. All readings were taken on same subject as in FIGS. 12 a-d, justminutes apart from one another (FIG. 13 a, 9:54 P.M.; FIG. 13 b, 10:01P.M.; FIG. 13 c 10:06 P.M.; FIG. 13 d 10:12 P.M.). Much greaterconsistency is observed in readings than among those in FIGS. 12 a-d.

Although this invention has been described with a certain degree ofparticularity, it is to be understood that the present disclosure hasbeen made only by way of illustration and that numerous changes in thedetails of construction and arrangement of parts may be resorted towithout departing from the spirit and the scope of the invention.

1. An article of manufacture, comprising: at least two sensors having anoffset potential of below about +/−1.0 mV; and a data gathering deviceconnected to the sensors capable of measuring the voltage differencebetween the electrodes.
 2. The article of claim 1, wherein at least twoof the sensors possess a sensing side having an AgCl coating on a Silversubstrate
 3. The article of claim 1, wherein the offset potential isbelow about +/−0.5 mV.
 4. The article of claim 1, wherein the offsetpotential is about +/−0.01 mV.
 5. The article of claim 1, wherein apre-applied conductive gel is disposed on the sensing side of thesensors.
 6. The article of claim 1, wherein the sensors are connected toa data gathering device via lead wires across a resistor of 0.5 to 500k-Ohms.
 7. The article of claim 1, wherein the sensors are less than 20mm in diameter.
 8. The article of claim 1, wherein the sensors are 10 mmin diameter.
 9. The article of claim 1, wherein the sensors aredisposable.
 10. The article of claim 1, wherein the sensors have anadhesive collar.
 11. A device suitable for detecting a shift in theautonomic nervous system, comprising: a sensor, wherein said sensor isutilized with at least one other sensor, and said sensor has an offsetpotential of less than 0.5 mV when used with said other sensor.
 12. Thedevice of claim 11, wherein the sensors have an exposed-to-gel sensingside of silver chloride coated silver.
 13. The device of claim 11,wherein the offset potential is below about +/−0.5 mV.
 14. The device ofclaim 11, wherein the offset potential is about +/−0.01 mV.
 15. Thedevice of claim 11, wherein a conductive gel is pre-applied to thesensor.
 16. The device of claim 11, wherein the sensor is less than 50mm in diameter.
 17. The device of claim 11, wherein the sensor is lessthan 20 mm in diameter.
 18. The device of claim 11, wherein the sensoris about 10 mm in diameter.
 19. The device of claim 11, wherein thesensor is disposable.
 20. The device of claim 11, wherein the sensor hasan adhesive collar.
 21. A method for detecting a shift in the autonomicnervous system, comprising: affixing at least two sensors having apaired offset potential of less than 0.5 mV to contralateral sides of ananimal or human; and measuring the voltage difference between saidsensors.
 22. The method of claim 21 wherein the voltage differential ismeasured continuously.
 23. The method of claim 21, wherein the voltagedifferential is recorded, displayed or both recorded and displayed by adata gathering device.
 24. The method of claim 21, wherein the voltagedifferential is correlated to a Visual Analogue Scale and self-reportedpain.
 25. The method of claim 21, wherein the method is used to diagnoseconditions of altered ANS function.
 26. The method of claim 21, whereinthe method is used to ascertain the effectiveness of medicine.
 27. Themethod of claim 21, wherein the method is used on a human.
 28. Themethod of claim 21, wherein the method is used on an animal.
 29. Themethod of claim 21, wherein at least one sensor is affixed to each handof a human.